1. Field of the Invention
The present invention relates generally to backlighting systems especially suitable for use with liquid crystal displays, and more particularly to (1) a specifically designed backlighting assembly capable of providing collimating backlight illumination; (2) a specifically designed arrangement for polarizing the collimated light exiting the backlighting assembly; and (3) an arrangement in cooperation with the backlighting assembly and its associated liquid crystal display for ensuring that the latter can be easily viewed from substantially all angles.
2. Description of the Related Art
Liquid crystal displays (LCDs) are commonly used in portable computer systems, televisions, and other electronic display devices. Large area, high performance LCDs require a source of lighting for operation. Backlighting the LCD has become the most popular source of light in personal computers, televisions, as well as projector type displays. In general, there is a need to obtain a sufficiently bright backlight level with as little power consumption as possible. Uniformity of the backlighting as well as small space for convenience of portability are also desirable. In most of the lighting systems, light is not collimated which makes it impossible for use in applications like, for example, triple supertwist nematic liquid crystal displays (TSTN) which need highly collimated backlighting. Although some approaches have been proposed to obtain collimated backlighting for the TSTN display, they all need a point light source and an optical system based on lenses and mirrors. Since a point light source is generally less efficient than a fluorescent lamp and requires a cooling system such as a fan, and optical systems based on lenses and mirrors take up a large space, techniques for highly collimated light sources presented heretofore were not practical for the backlighting of portable computers and flat television sets. For this reason, the TSTN and other stacked panel technology is limited to projector type display at this moment. On the other hand, as will be seen hereinafter, with the backlighting assembly designed in accordance with the present invention, a highly collimated light source which uses little space and consumes little power may be applied to techniques such as TSTN and make it suitable for colored display in portable computers as well as flat real time video displays.
In addition to the need for a relatively small, low powered but highly collimated backlighting arrangement for liquid crystal displays, there is a need to reduce the way in which viewing of a typical prior art liquid crystal display is dependent upon the angle at which it is viewed. As will also be seen hereinafter, a specific light diffusing plate member is combined with the backlighting assembly disclosed herein and the liquid crystal display itself for minimizing this angular dependence. A viewing angle insensitive LCD is particularly desirable for video applications such as "television on wall".
A particular shortcoming associated with liquid crystal displays resides in the fact that most LCDs require polarized light. Most polarizers are light inefficient, that is, at least half of the light is lost as a result of the polarizing process. As will be seen hereinafter, a specifically designed polarizer is combined with the backlighting assembly disclosed herein such that substantially all of the light exiting the backlighting assembly and entering the liquid crystal display is polarized.
With particular regard to the specific backlighting assemblies disclosed herein, two U.S. Patents are worth noting. They are U.S. Pat. Nos. 4,917,465 (Conner et al.) and 5,050,946 (Hathaway). This latter patent discloses a number of different backlighting assemblies for use with a liquid crystal display. In each of the embodiments illustrated, except one, a longitudinally extending light pipe is combined with a light source at one end thereof and means within or forming part of the light pipe for redirecting light entering one end thereof back out of the light pipe along one surface of the latter in confronting relationship with the liquid crystal display. In all of these embodiments, the light provided for use by the liquid crystal display is not highly collimated, certainly not to the degree achieved by the backlighting assembly of the present invention. In the Conner et al. patent, a number of backlighting arrangements are disclosed utilizing various lens systems. In most of these cases, a high degree of light collimation is not achieved. In other cases, while the embodiments illustrated generate collimated light, they do so by means of point light sources in combination with bulky lenses and mirrors.